The most important amendment going on the order paper today is the one in the names of Hilary Benn, Oliver Letwin and Yvette Cooper – because it is the one that would wrest control of shaping Brexit from the prime minister and deliver this control to MPs.
This is a coup against the PM, against the executive, so Theresa May is honour bound to oppose it, to instruct Tory MPs via a three-line whip to vote it down.
But it was clear from what Greg Clark, the business secretary said on my show last night, and what the Chancellor said in his spring statement yesterday, that important members of the Cabinet – them, plus Rudd and Gauke, for instance – support this revolt of the backbenches.
So the first question is whether Clark, Rudd and Gauke – plus other ministers desperate to avoid a no-deal Brexit – will have to rebel against the PM again by either abstaining on the Benn/Letwin amendment or backing it.
Probably not, I am reliably told. Since the movers of the motion are convinced they will win, even without ministerial support, and would rather keep their supporters inside the PM’s tent.
‘They are more useful to us in the government rather than out’ one of the leaders of the coup told me – in language that will further enrage Brexiter Tories, who fear they are being comprehensively outmanoeuvred by unreconstructed Remainers who are seeking to capture the Brexit citadel and deliver what they see as Brexit in Name Only.
There is of course deep pain for the prime minister in the confidence of Benn/Letwin/Cooper that they will triumph even without ministerial resignations, which is that she has lost control of her backbenches – and that significant numbers of Tories outside the payroll will disobey her.
So how does their disloyal amendment transfer power away from 10 Downing Street?
Well here is where it gets complicated. Bear with me.
The first thing it does is temporarily remove the PM’s power to set the agenda in parliament – in this instance on next Wednesday.
On that day a motion would be debated by MPs which if passed would then pave the way for what’s known as indicative votes on different versions of Brexit the following week – on another day when control of parliament’s agenda would be seized from the prime minister by backbenchers.
On this second full day of the backbenchers’ coup, MPs would then be able to table their own preferred routes through the Brexit mess. Those routes might include a no-deal Brexit, the so-called Malthouse Brexit (a ‘managed’ no-deal Brexit), Common Market 2.0 (the Norway model augmented by a customs ‘arrangement’ – don’t ask!), a referendum and so on.
And at the end of that day, all these options would be printed on bits of paper. And MPs would – in a secret ballot, to avoid gaming of the system – be able to put a tick next to any version of Brexit or even a no Brexit that they favour.
MPs would be able to vote for as many plans as they like. They would simply be asked to show which routes they would tolerate.
Now, the expectation is that after this day two of backbenchers’ control, there would not be a clear winner.
No single option would be backed by a majority of MPs – which seems the most likely outcome. Or there may be several which command a majority (in that, as I said, MPs could vote for as many Brexit plans as they like).
Either way, the chances are that backbenchers will have to seize control of a third day of business from the government, to whittle down the most popular options to just a single one that commands the majority of MPs.
And at that juncture the Prime Minister would be instructed to negotiate that outcome with Brussels and EU leaders.
By now you will have realised that this does genuinely represent an extraordinary and unprecedented undermining of the PM on the most important issue of this age and one of the most important issues of almost any age.
Her humiliation at that point would be complete.
Why would formerly loyal Tory MPs turn her into their puppet? Well it is because they are concerned that if they don’t, the alternative would be a no-deal Brexit – which, they fear, would wreak havoc on country and their party, from which neither would recover for many years.
And the reason they have to launch their coup today is because it has to be underway – they say – before the European Council in a week’s time, in that they are anxious EU leaders would not delay Brexit unless and until they can see MPs beginning the process of rallying towards a particular Brexit course.
So we are on the brink of history – the transmogrification of Theresa May into PINO, or Prime Minister in Name Only.
Robert Peston is ITV’s Political Editor. This article originally appeared on his Facebook page.